The present invention relates to a coating composition consisting of at least four components, comprising a component (I) comprising at least one oligomeric or polymeric resin containing functional groups which react with isocyanate groups, as binder (A), a component (II) comprising at least one polyisocyanate as crosslinking agent (F), and a component (III) which comprises water. The present invention additionally relates to a process for preparing these coating compositions and also to the use of the coating compositions in automotive OEM finishing, refinish, and for the coating of plastics, and also as topcoat materials or primer-surfacers.
Coating compositions of the abovementioned type in which component (III) contains no binders (A) are known from the patent U.S. Pat. No. 5,466,745. One of their uses is to produce clearcoats. The surfaces of these clearcoats, however, are still unable to satisfy every quality requirement, since they have pinholes and blisters.
Coating compositions of the abovementioned type in which component (III) comprises dissolved or dispersed binders (A) are known from the German patents DE-A-195 42 626 and DE-A-44 21 823. These known coating compositions already have comparatively few surface problems, such as popping marks or structuring, and as regards gloss, relaxation, spraying reliability, fullness, weathering stability, and other important technological properties they possess a good profile of properties.
The increasingly more stringent requirements of the market, however, are making it necessary to improve these known coating compositions still further in terms of their homogeneity, stability, handling, and popping limits. Moreover, the solvent content is to be lowered further than has been possible to date. Furthermore, the resulting coatings should have an even higher gasoline resistance and an even lower gray haze.
These known coating compositions or their component (III) comprise binders in dispersion or solution in water, which in the dissolved or dispersed state, especially on prolonged storage, are infested and destroyed by microorganisms, thereby rendering the component (III) in question of the coating compositions unusable and requiring disposal, which is a grave disadvantage both technically and economically.
If the component (III) affected is used anyway, it produces coatings, especially clearcoats, which are no longer in accordance with user requirements, especially in the automobile industry.
It is an object of the present invention to find a novel coating composition which no longer has the disadvantages depicted above but which instead is infested to a considerably reduced extent, if at all, by microorganisms and therefore has a relatively high storage stability of the component in question, with the advantageous properties of the known coating compositions being at least retained if not indeed improved further.
The invention accordingly provides the novel coating composition consisting of at least four components, comprising
(I) a component comprising at least one oligomeric or polymeric resin containing functional groups which react with isocyanate groups, as binder (A).
(II) a component comprising at least one polyisocyanate as crosslinking agent (F),
(III) a component which comprises water and is substantially free from acrylate copolymers (A) dispersed or dissolved therein, and
(IV) a finely divided solid component which comprises at least one water-soluble or -dispersible finely divided solid acrylate copolymer (A).
In the text below, the novel coating composition consisting of at least four components is referred to for the sake of brevity as the xe2x80x9ccoating composition of the inventionsxe2x80x9d.
The present invention further provides a process for preparing the coating compositions of the invention, and also provides for their use in automotive OEM finishing, refinish, and the coating of plastics, as topcoat materials or primer-surfacers.
The coating compositions of the invention are notable, surprisingly, for a profile of properties which is improved over the prior art in relation in particular to the gloss, fullness, low popping tendency, spraying reliability, and leveling, and also in respect of the weathering stability.
The particular advantage of the coating composition of the invention is firstly that component (III) is substantially-free from dissolved or dispersed acrylate copolymers (A), so that even on prolonged storage it is no longer infested by microorganisms, or only to an extent which does not perceptibly impair its performance properties. Secondly, the particular advantage of the coating compositions of the invention is that component (IV) may be stored for a particularly long time without detriment to its performance properties. Furthermore, as a finely divided solid, it can be added to the coating composition, especially to component (III), in a particularly simple and easy fashion.
It is surprising, furthermore, that the coating compositions of the invention comprising said at least four components may be prepared simply by mixing without the need for complicated mixing and/or dispersing apparatus as described, for example, in the German patent DE-A-195 10 651. The coating compositions of the invention are therefore suitable in particular for the field of automotive refinish, since they can be prepared by the painter by simple mixing of the components directly prior to their application and can be cured at low temperatures.
A further advantage is that the coating compositions of the invention prepared from said at least four components contain only a small fraction of volatile organic solvents, despite the fact that the coating compositions are prepared using crosslinkers and binders dispersed and/or dissolved in organic media.
Moreover, the coating compositions of the invention ensure a high level of variability, since it is possible to use not only the crosslinking agents, pigments and additives that are recommended for aqueous coating compositions but also those used in conventional systems.
Finally, a feature of the inventive components of the coating compositions of the invention is a very good storage stability, which corresponds to that of conventional coating compositions.
The constituent of the coating composition of the invention that is essential to the invention is its finely divided solid component (IV), which comprises at least one water-soluble or -dispersible finely divided solid acrylate copolymer (A).
The finely divided solid acrylate copolymers (A) for use in accordance with the invention are oligomeric or polymeric resins containing functional groups which react with isocyanate groups.
Examples of suitable functional groups for use in accordance with the invention that react with isocyanate groups are epoxy, amino, thio and/or hydroxyl groups, of which the hydroxyl groups are particularly advantageous and are therefore particularly preferred in accordance with the invention.
Accordingly, the finely divided solid acrylate copolymers (A) which are preferred in accordance with the invention comprise hydroxyl-containing oligomeric or polymeric resins.
Besides the hydroxyl groups, the finely divided solid acrylate copolymers (A) may contain other functional groups as well, such as acryloyl, amide, imide, carbonate or epoxide groups.
In accordance with the invention, the finely divided solid acrylate copolymers (A), viewed per se, are dispersible or soluble in water.
Examples of suitable water-soluble or water-dispersible finely divided solid acrylate copolymers (A) contain alternatively
(i) functional groups which can be converted into cations by neutralizing agents and/or quaternizing agents, and/or cationic groups,
or
(ii) functional groups which can be converted into anions by neutralizing agents, and/or anionic groups,
and/or
(iii) nonionic hydrophilic groups.
Examples of suitable functional groups (i) for use in accordance with the invention that can be converted into cations by neutralizing agents and/or quaternizing agents are primary, secondary or tertiary amino groups, secondary sulfide groups or tertiary phosphine groups, especially tertiary amino groups or secondary sulfide groups.
Examples of suitable cationic groups (i) for use in accordance with the invention are primary, secondary, tertiary or quaternary ammonium groups, tertiary sulfonium groups or quaternary phosphonium groups, preferably quaternary ammonium groups or tertiary sulfonium groups, but especially tertiary sulfonium groups.
Examples of suitable functional groups (i) for use in accordance with the invention that may be converted into anions by neutralizing agents are carboxylic acid, sulfonic acid or phosphonic acid groups, especially carboxylic acid groups.
Examples of suitable anionic groups (i) for use in accordance with the invention are carboxylate, sulfonate or phosphonate groups, especially carboxylate groups.
Examples of suitable nonionic hydrophilic groups (i) for use in accordance with the invention are polyether groups, especially poly(alkylene ether) groups.
Regarding the preparability, handling and particularly advantageous properties of the coating compositions of the invention prepared using them, the finely divided solid acrylate copolymers (A) which contain the anion-forming groups and/or anions (ii), especially the carboxylic acid and/or the carboxylate groups, afford very particular advantages, and so are used with very particular preference in accordance with the invention.
Examples of very particularly, preferred finely divided solid acrylate copolymers (A) of the last-mentioned type, for use in accordance with the invention, are
(A1) the acrylate copolymers (A1) which are described below, contain hydroxyl groups and carboxylic acid and/or carboxylate groups, and have a number average molecular weight Mn of between 1000 and 30,000 daltons, an OH number of from 40 to 200 mg KOH/g, and an acid number of from 5 to 150 mg KOH/g.
Owing to their comparatively simple preparation, their easy handling, their advantageous profile of properties, and the particular advantages of the coating compositions of the invention produced using them, very particular preference is given to using the finely divided solid acrylate copolymers (A1). Moreover it is found in many cases that the problems of infestation by microorganisms can be solved substantially and in many cases even completely simply by using the acrylate copolymers (A1) in finely divided solid form.
Suitable finely divided solid acrylate copolymers (A1) include all acrylate copolymers having the stated OH numbers, acid numbers, molecular weights, and viscosities.
In particular, use is made of finely divided solid acrylate copolymers (A1) obtainable in the presence of at least one polymerization initiator by bulk polymerization, solution polymerization in an organic solvent or solvent mixture, by emulsion polymerization or precipitation polymerization in water of
a1) a (meth)acrylic ester which is substantially free from acid groups and is different from but copolymerizable with (a2), (a3), (a4), (a5), and (a6), or a mixture of such monomers (a1),
a2) an ethylenically unsaturated monomer which carries at least one hydroxyl group per molecule and is substantially free from acid groups, and which is copolymerizable with (a1), (a3), (a4), (a5), and (a6) but different from (a5), or a mixture of such monomers (a2,
a3) an ethylenically unsaturated monomer which carries per molecule at least one acid group which can be converted into the corresponding acid anion group, and which is copolymerizable with (a1), (a2), (a4), (a5), and (a6), or a mixture of such monomers (a3), and
a4) if desired, one or more vinyl esters of alpha-branched monocarboxylic acids having from 5 to 18 carbon atoms per molecule, and/or
a5) if desired, at least one reaction product of acrylic acid and/or methacrylic acid with the glycidyl ester of an alpha-branched monocarboxylic acid having from 5 to 18 carbon atoms per molecule, or instead of the reaction product an equivalent amount of acrylic and/or methacrylic acid which is then reacted during or after the polymerization reaction with the glycidyl ester of an alpha-branched monocarboxylic acid having from 5 to 18 carbon atoms per molecule,
a6) if desired, an ethylenically unsaturated monomer which is substantially free from acid groups, is copolymerizable with (a1), (a2), (a3), (a4), and (a5) but different from (a1), (a2), (a4), and (a5), or a mixture of such monomers (a6),
the nature and amount of (a1), (a2), (a3), (a4), (a5), and (a6) being selected so that the polyacrylate resin (A1) has the desired OH number, acid number, and molecular weight.
To prepare the finely divided solid acrylate copolymers (A1) it is possible as component (a1) to use any (meth)acrylic alkyl or cycloalkyl ester which is copolymerizable with (a2), (a3), (a4), (a5), and (a6) and which has up to 20 carbon atoms in the alkyl radical, especially methyl, ethyl, propyl, n-butyl, sec-butyl, tert-butyl, hexyl, ethylhexyl, stearyl and lauryl acrylate or methacrylate; cycloaliphatic (meth)acrylic esters, especially cyclohexyl, isobornyl, dicyclopentadienyl, octahydro-4,7-methano-1H-indene-methanol or tert-butylcyclohexyl (meth)acrylate; (meth)acrylic oxaalkyl esters or oxacycloalkyl esters such as ethyl triglycol (meth)acrylate and methoxyoligoglycol (meth)acrylate having a molecular weight Mn of preferably 550; or other ethoxylated and/or propoxylated, hydroxyl-free (meth)acrylic acid derivatives. These may contain minor amounts of (meth)acrylic alkyl or cycloalkyl esters of higher functionality, such as ethylene glycol, propylene glycol, diethylene glycol, dipropylene glycol, butylene glycol, 1,5-pentanediol, 1,6-hexanediol, octahydro-4,7-methano-1H-indenedimethanol or 1,2-, 1,3- or 1,4-cyclohexanediol di(meth)acrylate; trimethylolpropane di- or tri(meth)acrylate; or pentaerythritol di-, tri- or tetra(meth)acrylate. In the context of the present invention, minor amounts of monomers of relatively high functionality are understood as being amounts which do not lead to crosslinking or gelling of the polyacrylate resins.
As component (a2) it is possible to use ethylenically unsaturated monomers which carry at least one hydroxyl group per molecule and are substantially free from acid groups, and are copolymerizable with (a1), (a2), (a3), (a4), (a5), and (a6) but different from (a5), such as hydroxyalkyl esters of acrylic acid, methacrylic acid or another alpha,beta-ethylenically unsaturated carboxylic acid which are derived from an alkylene glycol which is esterified with the acid or are obtainable by reacting the acid with an alkylene oxide, especially hydroxyalkyl esters of acrylic acid, methacrylic acid, ethacrylic acid, crotonic acid, maleic acid, fumaric acid or itaconic acid in which the hydroxyalkyl group contains up to 20 carbon atoms, such as 2-hydroxyethyl, 2-hydroxypropyl, 3-hydroxypropyl, 3-hydroxybutyl, 4-hydroxybutyl acrylate, methacrylate, ethacrylate, crotonate, maleate, fumarate or itaconate; 1,4-bis(hydroxymethyl)cyclohexane, octahydro-4,7-methano-1H-indenedimethanol, or methylpropanediol monoacrylate, monomethacrylate, monoethacrylate, mono-crotonate, monomaleate, monofumarate or monoitaconate; or reaction products of these hydroxyalkyl esters and cyclic esters, such as epsilon-caprolactone, for example; or olefinically unsaturated alcohols such as allyl alcohol or polyols such as trimethylolpropane monoallyl or diallyl ether or pentaerythritol monoallyl, diallyl or triallyl ether. Regarding these monomers (a2) of higher functionality, the comments made regarding the higher-functional monomers (a1) apply analogously. The fraction of trimethylolpropane monoallyl ether is usually from 2 to 10% by weight, based on the overall weight of the monomers (a1) to (a6) used to prepare the polyacrylate resin. In addition, however, it is also possible to add from 2 to 10% by weight, based on the overall weight of the monomers used to prepare the polyacrylate resin, of trimethylolpropane monoallyl ether to the finished polyacrylate resin. The olefinically unsaturated polyols, such as trimethylolpropane monoallyl ether in particular, may be used as sole hydroxyl-containing monomers, but in particular may also be used proportionally in combination with other of the hydroxyl-containing monomers mentioned.
As component (a3), it is possible to use any ethylenically unsaturated monomer which carries at least one acid group, preferably a carboxyl group, per molecule and is copolymerizable with (a1), (a2), (a4), (a5), and (a6), or a mixture of such monomers. Acrylic acid and/or methacrylic acid are used with particular preference as component (a3). It is, however, also possible to use other ethylenically unsaturated carboxylic acids having up to 6 carbon atoms in the molecule. Examples of such acids are ethacrylic acid, crotonic acid, maleic acid, fumaric acid, and itaconic acid. A further possibility is to use ethylenically unsaturated sulfonic or phosphonic acids, and/or their partial esters, as component (a3). Further suitable components (a3) include mono(meth)acryloyloxyethyl maleate, succinate, and phthalate.
As component (a4) use is made of one or more vinyl esters of alpha-branched monocarboxylic acids having from 5 to 18 carbon atoms in the molecule. The branched monocarboxylic acids may be obtained by reacting formic acid or carbon monoxide and water with olefins in the presence of a liquid, strongly acidic catalyst; the olefins may be cracking products of paraffinic hydrocarbons, such as mineral oil fractions, and may contain both branched and straight-chain acylic and/or cycloaliphatic olefins. The reaction of such olefins with formic acid or with carbon monoxide and water produces a mixture of carboxylic acids in which the carboxyl groups are located predominantly on a quaternary carbon atom. Other olefinic starting materials are, for example, propylene trimer, propylene tetramer, and diisobutylene. Alternatively, the vinyl esters may be prepared conventionally from the acids, by reacting the acid with acetylene, for example. Particular preference is givenxe2x80x94owing to their ready availabilityxe2x80x94to using vinyl esters of saturated aliphatic monocarboxylic acids having 9 to 11 carbon atoms that are branched on the alpha carbon atom.
As component (a5), the reaction product of acrylic acid and/or methacrylic acid with the glycidyl ester of an alpha-branched monocarboxylic acid having from 5 to 18 carbon atoms per molecule is used. Glycidyl esters of highly branched monocarboxylic acids are available under the trade name Cardura. The reaction of the acrylic or methacrylic acid with the glycidyl ester of a carboxylic acid having a tertiary alpha carbon atom may take place before, during or after the polymerization reaction. As component (a5) it is preferred to use the reaction product of acrylic and/or methacrylic acid with the glycidyl ester of Versatic acid. This glycidyl ester is available commercially under the name Cardura E10.
As component (a6) it is possible to use all ethylenically unsaturated monomers that are substantially free from acid groups and are copolymerizable with (a1), (a2), (a3), (a4), and (a5) but different from (a1), (a2), (a3), and (a4), or mixtures of such monomers (a6) Suitable components (a6) include
olefins such as ethylene, propylene, 1-butene, 1-pentene, 1-hexene, cyclohexene, cyclopentene, norbornene, butadiene, isoprene, cyclopentadiene and/or dicyclopentadiene;
(meth)acrylamides such as (meth)acrylamide, N-methyl-, N,N-dimethyl-, N-ethyl-, N,N-diethyl-, N-propyl-, N,N-dipropyl, N-butyl-, N,N-dibutyl-, N-cyclohexyl- and/or N,N-cyclohexyl-methyl-(meth)acrylamide;
monomers containing epoxide groups, such as the glycidyl ester of acrylic acid, methacrylic acid, ethacrylic acid, crotonic acid, maleic acid, fumaric acid and/or itaconic acid;
vinylaromatic hydrocarbons, such as styrene, alpha-alkylstyrenes, especially alpha-methyl-styrene, and/or vinyltoluene;
nitriles such as acrylonitrile and/or methacrylo-nitrile;
vinyl compounds such as vinyl chloride, vinyl fluoride, vinylidene dichloride, vinylidene difluoride; N-vinylpyrrolidone; vinyl ethers such as ethyl vinyl ether, n-propyl vinyl ether, isopropyl vinyl ether, n-butyl vinyl ether, isobutyl vinyl ether and/or vinyl cyclohexyl ether; vinyl esters such as vinyl acetate, vinyl propionate, vinyl butyrate, vinyl pivalate and/or the vinyl ester of 2-methyl-2-ethylheptanoic acid; and/or
polysiloxane macromonomers which have a number average molecular weight Mn of from 1000 to 40,000, preferably from 2000 to 20,000, with particular preference from 2500 to 10,000, and in particular from 3000 to 7000, and contain on average from 0.5 to 2.5, preferably from 0.5 to 1.5, ethylenically unsaturated double bonds per molecule, as described in DE-A 38 07 571 on pages 5 to 7, in DE-A 37 06 095 in columns 3 to 7, in EP-B-0 358 153 on pages 3 to 6, in U.S. Pat. No. 4,754,014 in columns 5 to 9, in DE-A 44 21 823, or in the international patent application WO 92/122615 on page 12, line 18 to page 18, line 10, or acryloxysilane-containing vinyl monomers, preparable by reacting hydroxy-functional silanes with epichlorohydrin and then reacting that reaction product with methacrylic acid and/or hydroxyalkyl esters of (meth)acrylic acid.
It is preferred to use vinylaromatic hydrocarbons.
It is of advantage to use the polysiloxane macromonomers (a6) together with other monomers (a6). In this case the amount of the polysiloxane macromonomer or macromonomers (a6) for modifying the acrylate copolymers (A1) should be less than 5% by weight, preferably from 0.05 to 2.5% by weight, with particular preference from 0.05 to 0.8% by weight, based in each case on the overall weight of the monomers used to prepare the copolymer (A1). The use of such polysiloxane macromonomers leads to an improvement in the slip of the coatings of the invention.
The nature and amount of components (a1) to (a6) is selected such that the finely divided solid acrylate copolymer (A1) has the desired OH number, acid number, and glass transition temperature. Finely divided solid acrylate copolymers (A1) used with particular preference are obtained by polymerizing
(a1) from 20 to 60% by weight, preferably from 30 to 50% by weight, of component (a1),
(a2) from 10 to 50% by weight, preferably from 15 to 40% by weight, of component (a2),
(a3) from 1 to 15% by weight, preferably from 1 to 8% by weight, of component (a3),
(a4) from 0 to 25% by weight, preferably from 5 to 15% by weight, of component (a4),
(a5) from 0 to 25% by weight, preferably from 5 to 15% by weight, of component (a5), and
(a6) from 5 to 30% by weight, preferably from 10 to 20% by weight, of component (a6),
the sum of the weight fractions of components (a1) to (a6) being in each case 100% by weight.
The water-soluble or water-dispersible finely divided solid acrylate copolymers (A) for use in accordance with the invention may be present individually or as a mixture.
If they are to be used in a mixture, it should be ensured that finely divided solid acrylate copolymers (A) containing functional groups (i) are not combined with finely divided solid acrylate copolymers (A) containing functional groups (ii), since this may lead to the formation of insoluble electrolyte complexes.
Furthermore, the finely divided solid acrylate copolymers (A) may additionally comprise binders (A) which per se are not dispersible or soluble in water but which can be dispersed in water in the presence of the water-soluble or dispersible acrylate copolymers (A). Examples of suitable binders (A) not soluble or dispersible in water come from the oligomer and/or polymer classes described below, with the proviso that they contain no hydrophilic functional groups (i), (ii) or (iii) or only so few such groups as not to result in water-solubility or -dispersibility.
If, in the preparation of the coating compositions of the invention, the mixing of the components (I), (II), (III), and (IV) is to take place by manual stirring, it is of advantage for the coating composition of the invention if the finely divided solid acrylate copolymers (A) are selected such that their 50% strength solution in ethoxyethyl propionate at 23xc2x0 C. has a viscosity of xe2x89xa610 dPas. Where mechanical mixing is to take place, it is possible to use binders (A) of higher viscosity, whose 50% strength solution in ethoxyethyl propionate at 23xc2x0 C has a viscosity of xe2x89xa6100 dpas. The viscosity is limited at the top end only by the performance capacity of the mixing equipment.
The particle size of the finely divided solid acrylate copolymers (A) is not critical. What is important is that the particle size is not made so small that the particles tend to agglomerate and/or become respirable, or so large that redissolution or redispersion is hindered or prevented. In accordance with the invention, particle sizes of from 5 to 500 xcexcm are of advantage.
The preparation of the finely divided solid acrylate copolymers (A) has no special features in terms of its method but instead takes place in accordance with, the customary and known methods of polymerization in bulk, solution or emulsion or by suspension polymerization or precipitation polymerization and drying of the resulting acrylate copolymers (A) with the aid of customary and known methods and apparatus and under conditions which ensure the formation of finely divided solid products. Examples of suitable drying methods are spray drying, freeze drying, and precipitation from solution, emulsion or suspension.
In many cases it is of advantage, after preparing the acrylate copolymers (A), to add to them aqueous media, which may include at least one of the neutralizing agents (D) described below, in order to convert them into a secondary dispersion, which is then dried.
In the case of polymerization in solution, solvents are used which do not pose a hindrance to drying but are instead easy to remove from the acrylate copolymers (A). It is preferred to use solvents having a comparatively high vapor pressure. The same applies to the cosolvents which may be used in the emulsion, suspension or precipitation polymerization or for preparing the secondary dispersions, or to the nonsolvents which are used for precipitation.
For the preparation of the acrylate copolymers (A1) used with preference in accordance with the invention it is advantageous to use polymerization initiators.
Examples of suitable polymerization initiators are initiators which form free radicals, such as tert-butyl peroxyethylhexanoate, benzoyl peroxide, di-tert-amyl peroxide, azobisisobutyronitrile, and tert-butyl per-benzoate, for example. The initiators are used preferably in an amount from 1 to 25% by weight, with particular preference from 2 to 10% by weight, based on the overall weight of the monomers.
The polymerization is appropriately conducted at a temperature from 80 to 200xc2x0 C., preferably from 110 to 180C. Preferred solvents used are ethoxyethyl propionate and isopropoxypropanol.
The acrylate copolymer (A1) is preferably prepared by a two-stage process, since in that way the resultant coating compositions of the invention possess better processing properties. It is therefore preferred to use acrylate copolymers (A1) which are obtainable by
1. polymerizing a mixture of (a1), (a2), (a4), (a5), and (a6), or a mixture of portions of components (a1), (a2), (a4), (a5), and (a6), in an organic solvent and/or in one of the reactive diluents mentioned below,
2. after at least 60% by weight of the mixture consisting of (a1), (a2), (a4), (a5), and, where used, (a6) have been added, adding (a3) and any remainder of components (a1), (a2), (a4), (a5), and (a6), and continuing polymerization, and
3. after the end of the polmerization, subjecting the resulting polyacrylate resin if desired to at least partial neutralization, i.e., converting the acid groups into the corresponding acid anion groups.
In addition, however, it is also possible to include components (a4) and/or (a5) in the initial charge together with at least part of the solvent, and to meter in the remaining components. Moreover, it is also possible for components (a4) and/or (a5) to be included only in part in the initial charge, together with at least part of the solvent, and for the remainder of these components to be added as described above. Preferably, for example, at least 20% by weight of the solvent and about 10% by weight of component (a4) and (a5), and also, if desired, portions of components (a1) and (a6), are included in the initial charge.
Preference is also given to preparing the acrylate copolymers (A1) by means of a two-stage process whose first stage lasts from 1 to 8 hours, preferably from 1.5 to 4 hours, and in which a mixture of (a3) and any remainder of components (a1), (a2), (a4), (a5), and (a6) is added over the course of from 20 to 120 minutes, preferably over the course of from 30 to 90 minutes. Following the end of the addition of the mixture of (a3) and any remainder of components (a1), (a2), (a4), (a5), and (a6), polymerization is continued until all of the monomers used have undergone substantially complete reaction. The second stage in this process may immediately follow the first. Alternatively, the second stage may be commenced after a certain time, for example after from 10 minutes to 10 hours.
The amount and rate of addition of the initiator are preferably chosen so as to give a polyacrylate resin (A1) having a number average molecular weight Mn of from 1000 to 30,000 daltons. It is preferred to commence the initiator feed at a certain time, generally about 15 minutes, before the feeding of the monomers. Preference is given, further, to a process in which the addition of initiator is commenced at the same point in time as the addition of the monomers and is ended about half an hour after the addition of the monomers has ended. The initiator is preferably added in a constant amount per unit time. Following the end of the addition of initiator, the reaction mixture is held at polymerization temperature until (generally 1.5 hours) all of the monomers used have undergone substantially complete reaction. xe2x80x9cSubstantially complete reactionxe2x80x9d is intended to denote that preferably 100% by weight of the monomers used have undergone reaction but that it is also possible for a small residual monomer content of not more than up to about 0.5% by weight, based on the weight of the reaction mixture, to remain unreacted.
Preferably, the monomers for preparing the acrylate copolymers (A1) are polymerized at a polymerization solids which is not too high, preferably at a polymerization solids of from 80 to 50% by weight, based on the comonomers, and then the solvents are removed in part by distillation, so that the resulting acrylate copolymer solutions (A1) have a solids content of preferably from 100 to 60% by weight.
The preparation of the finely divided solid acrylate copolymers (A1), especially the finely divided solid acrylate copolymers (A1) for use in accordance with the invention takes place by means of the methods of continuous or batchwise copolymerization that are known and customary in the polymers field, under atmospheric pressure or superatmospheric pressure, in stirred tanks, autoclaves, tube reactors or Taylor reactors.
Examples of suitable (co)polymerization processes for preparing the acrylate copolymers (A1) are described in the patents DE-A-197 09 465, DE-C-197 09 476, DE-A-28 48 906, DE-A-195 24 182, EP-A-0 554 783, WO 95/27742 or WO 82/02387.
Taylor reactors are advantageous.
Taylor reactors, which serve to convert substances under the conditions of Taylor flow, are known. They consist substantially of two coaxial concentric cylinders of which the outer is fixed and the inner rotates. The reaction space is the volume formed by the gap between the cylinders. Increasing angular velocity xcfx89i of the inner cylinder is accompanied by a series of different flow patterns which are characterized by a dimensionless parameter, known as the Taylor number Ta. In addition to the angular velocity of the stirrer, the Taylor number is also dependent on the kinematic viscosity v of the fluid in the gap and on the geometric parameters, the external radius of the inner cylinder ri, the internal radius of the outer cylinder ro, and the gap width d, the difference between the two radii, in accordance with the following formula:
Ta=xcfx89irid vxe2x88x921(d/ri)xc2xdxe2x80x83xe2x80x83(I)
where d=roxe2x88x92ri.
At low angular velocity, the laminar Couette flow, a simple shear flow, develops. If the rotary speed of the inner cylinder is increased further, then, above a critical level, alternately contrarotating vortices (rotating in opposition) occur, with axes along the peripheral direction. These vortices, called Taylor vortices, are rotationally symmetric and have a diameter which is approximately the same size as the gap width. Two adjacent vortices form a vortex pair or vortex cell.
The basis for this behavior is the fact that, in the course of rotation of the inner cylinder with the outer cylinder at rest, the fluid particles that are near to the inner cylinder are subject to a greater centrifugal force than those at a greater distance from the inner cylinder. This difference in the acting centrifugal forces displaces the fluid particles from the inner to the outer cylinder. The centrifugal force acts counter to the viscosity force, since for the motion of the fluid particles it is necessary to overcome the friction. Any increase in the rotary speed is accompanied by an increase in the centrifugal force as well. The Taylor vortices are formed when the centrifugal force exceeds the stabilizing viscosity force.
In the case of Taylor flow with a low axial flow, each vortex pair passes through the gap, with only a low level of mass transfer between adjacent vortex pairs. Mixing within such vortex pairs is very high, whereas axial mixing beyond the pair boundaries is very low. A vortex pair may therefore be regarded as a stirred tank in which there is thorough mixing. Accordingly, the flow system behaves as an ideal flow tube in that the vortex pairs pass through the gap with constant residence time, like ideal stirred tanks.
Of advantage in accordance with the invention here are Taylor reactors having an external reactor wall located within which there is a concentrically or eccentrically disposed rotor, a reactor floor, and a reactor lid, which together define the annular reactor volume, at least one means for metered addition of reactants, and a means for the discharge of product, where the reactor wall and/or the rotor are or is geometrically designed in such a way that the conditions for Taylor flow are met over substantially the entire reactor length in the reactor volume, i.e., in such a way that the annular gap broadens in the direction of flow traversal.
The further essential constituent of the coating compositions of the invention is component (I). It comprises at least one binder (A) containing functional groups which react with isocyanate groups. Suitable functional groups are all those described above in connection with component (IV).
Examples of suitable binders (A) are linear and/or branched and/or block, comb and/or random poly(meth)acrylates or acrylate copolymers, polyesters, alkyds, polyurethanes, acrylated polyurethanes, acrylated polyesters, poly-lactones, polycarbonates, polyethers, epoxy resin-amine adducts, (meth)-acrylatediols, partially saponified polyvinyl esters or polyureas, of which the acrylate copolymers, the polyesters, the polyurethanes, the polyethers, and the epoxy resin-amine adducts are particularly advantageous and are therefore used with particular preference.
Regarding the preparability, the handling and the particularly advantageous properties of the coating compositions of the invention that are prepared using them, the acrylate copolymers, the polyesters and/or the polyurethanes, but in particular the acrylate copolymers, afford very particular advantages, and so are used with very particular preference in accordance with the invention.
Where binders (A) which per se are not water-soluble or water-dispersible are used in component (I), it should be ensured that, by way of component (III) and/or (IV), the amount of water-soluble or water-dispersible binders (A) introduced into the coating composition of the invention is sufficient for the binders (A) overall to form a stable dispersion.
In component (I) as well, particular preference is given to using the above-described acrylate copolymers (A1) and also the polyester resins (A2) and/or polyurethane resins (A3) described below.
It is very particularly preferred to use the acrylate copolymers (A1) which have been prepared in what are known as reactive diluents as solvents, which are not separated off after the copolymerization. These reactive diluents participate in the reaction with the crosslinking component (II).
Examples of suitable thermally crosslinkable reactive diluents are branched, cyclic and/or acyclic C9-C16 alkanes functionalized with at least two hydroxyl groups, preferably dialkyloctanediols, especially the positionally isomeric diethyloctanediols.
Further examples of suitable thermally crosslinkable reactive diluents are oligomeric polyols obtainable by hydroformylation and subsequent hydrogenation of oligomeric intermediates themselves obtained by metathesis reactions of acyclic monoolefins and cyclic monoolefins; examples of suitable cyclic monoolefins are cyclobutene, cyclopentene, cyclohexene, cyclooctene, cycloheptene, norbornene, and 7-oxanorbornene; examples of suitable acyclic monoolefins are contained in hydrocarbon mixtures obtained in petroleum processing by cracking (C5 cut); examples of suitable oligomeric polyols for use in accordance with the invention have a hydroxyl number (OHN) of from 200 to 450, a number average molecular weight Mn of from 400 to 1000, and a mass average molecular weight Mw of from 600 to 1100.
Further examples of suitable thermally crosslinkable reactive diluents are hyperbranched compounds having a tetrafunctional central group, derived from ditrimethylolpropane, diglycerol, ditrimethylolethane, pentaerythritol, tetrakis(2-hydroxyethyl)methane, tetrakis(3-hydroxypropyl)methane or 2,2-bishydroxy-methyl-1,4-butanediol (homopentaerythritol). These reactive diluents may be prepared by the customary and known methods of preparing hyperbranched and dendrimeric compounds. Suitable synthesis methods are described, for example, in the patents WO 93/17060 and WO 96/12754 or in the book by G. R. Newkome, C. N. Moorefield and F. Vxc3x6gtle, xe2x80x9cDendritic Molecules, Concepts, Syntheses, Perspectivesxe2x80x9d, VCH, Weinheim, N.Y., 1996.
Further examples of suitable reactive diluents are polycarbonatediols, polyesterpolyols, poly(meth)-acrylatediols or hydroxy-containing polyaddition products.
Examples of suitable isocyanate-reactive solvents are butyl glycol, 2-methoxypropanol, -n-butanol, methoxy-butanol, n-propanol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol diethylene ether, diethylene glycol monobutyl ether, trimethylolpropane, ethyl 2-hydroxypropionate or 3-methyl-3-methoxybutanol and also derivatives based on propylene glycol, e.g., ethoxyethyl propionate, isopropoxypropanol or methoxypropyl acetate.
Said reactive diluents, especially the functionalized alkanes, and/or the isocyanate-reactive solvents may also be present in component (III).
Suitable polyester resins (A2) include all polyesters having the above-indicated OH numbers, acid numbers, molecular weights, and viscosities.
Use is made in particular of polyester resins (A2) obtainable by reacting
p1), optionally sulfonated polycarboxylic acids or their esterifiable derivatives, together if desired with monocarboxylic acids,
p2) polyols, together if desired with monools,
p3) if desired, further, modifying components, and
p4) if desired, a component which is reactive with the reaction product of (p1), (p2) and, where used, (p3).
Examples that may be given of polycarboxylic acids that may be used as component (p1) are aromatic, aliphatic, and cycloaliphatic polycarboxylic acids. As component (p1) it is preferred to use aromatic and/or aliphatic polycarboxylic acids.
Examples of suitable polycarboxylic acids are phthalic acid, isophthalic acid, terephthalic acid, phthalic, isophthalic or terephthalic monosulfonate, halophthalic acids, such as tetrachlorophthalic or tetrabromophthalic acid, adipic acid, glutaric acid, azelaic acid, sebacic acid, fumaric acid, maleic acid, trimellitic acid, pyromellitic acid, tetrahydrophthalic acid, hexahydrophthalic acid, 1,2-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, 4-methylhexahydrophthalic acid, endomethylenetetrahydrophthalic acid, tricyclodecanedicarboxylic acid, endoethylenehexahydrophthalic acid, camphoric acid, cyclohexanetetracarboxylic acid, or cyclobutanetetracarboxylic acid. The cycloaliphatic polycarboxylic acids may be used either in their cis or in their trans form or as a mixture of both forms. Also suitable are the esterifiable derivatives of the aforementioned polycarboxylic acids, such as their monoesters or polyesters with aliphatic alcohols having from 1 to 4 carbon atoms or hydroxy alcohols having from 1 to 4 carbon atoms, for example. It is also possible to use the anhydrides of the abovementioned acids, where they exist.
If desired, together with the polycarboxylic acids it is also possible to use monocarboxylic acids, such as benzoic acid, tert-butylbenzoic acid, lauric acid, isononanoic acid, and fatty acids of naturally occurring oils, for example. Isononanoic acid is a preferred monocarboxylic acid used.
Suitable alcohol components (p2) for preparing the polyester (A2) are polyhydric alcohols, such as ethylene glycol, propanediols, butanediols, hexanediols, neopentyl hydroxypivalate, neopentyl glycol, diethylene glycol, cyclohexanediol, cyclohexanedimethanol, trimethylpentanediol, ethylbutylpropanediol, ditrimethylolpropane, trimethylolethane, trimethylolpropane, glycerol, pentaerythritol, dipentaerythritol, trishydroxyethyl isocyanate, polyethylene glycol, polypropylene glycol, alone or together with monohydric alcohols, such as butanol, octanol, lauryl alcohol, cyclohexanol, tert-butylcyclohexanol, ethoxylated and/or propoxylated phenols, for example.
Compounds suitable as component (p3) for preparing the polyesters (A2) include in particular those having a group which is reactive toward the functional groups of the polyester, with the exception of the compounds specified as component (p4). As modifying component (p3) it is preferred to use polyisocyanates and/or diepoxide compounds, and also, if desired, monoisocyanates and/or monoepoxide compounds. Suitable components (p3) are described, for example, in DE-A-40 24 204 on page 4, lines 4 to 9.
Compounds suitable as component (p4) for preparing the polyesters (A2) are those compounds which in addition to a group that is reactive toward the functional groups of the polyester (A2) also contain a tertiary amino group, examples including monoisocyanates containing at least one tertiary amino group, or mercapto compounds containing at least one tertiary amino group. For details, refer to DE-A-40 24 204, page 4, lines 10 to 49.
The polyester resins (A2) are prepared in accordance with the known methods of esterification, as is described, for example, in DE-A-40 24 204, page 4, lines 50 to 65. This reaction takes place usually at temperatures between 180 and 280xc2x0 C., in the absence or presence of an appropriate esterification catalyst, such as lithium octoate, dibutyltin oxide, dibutyltin dilaurate or para-toluenesulfonic acid, for example.
The polyester resins (A2) are normally prepared in the presence of small amounts of an appropriate solvent as entrainer. Examples of entrainers used include aromatic hydrocarbons, such as xylene in particular, and (cyclo aliphatic hydrocarbons, e.g. cyclohexane or methylcyclohexane.
It is particularly preferred to use polyester resins (A2) which have been prepared by a two-stage process, by first preparing a hydroxyl-containing polyester having an OH number of from 100 to 300 mg KOH/g, an acid number of less than 10 mg KOH/g, and a number average molecular weight Mn of from 500 to 2000 daltons, which is then reacted in a second stage with carboxylic anhydrides to give the desired polyester resin (A2). The amount of carboxylic anhydrides in this case is chosen so that the resulting polyester resin (A2) has the desired acid number. Acid anhydrides suitable for this reaction are all those commonly used, such as hexahydrophthalic anhydride, trimellitic anhydride, pyromellitic anhydride, phthalic anhydride, camphoric anhydride, tetrahydrophthalic anhydride, succinic anhydride, and mixtures of these and/or other anhydrides, and especially anhydrides of aromatic polycarboxylic acids, such as trimellitic anhydride, for example.
It is possible if desired for the acrylate copolymer (A1) to have been prepared at least in part in the presence of the polyester resin (A2). In this case, advantageously at least 20% by weight and with particular advantage from 40 to 80% by weight of the acrylate copolymer (A1) are prepared in the presence of the polyester resin (A2). Any remainder of the acrylate copolymer (A1) is added subsequently to the component (I). In this case it is possible for this already polymerized resin to have the same monomer composition as the acrylate copolymer (A1) synthesized in the presence of the polyester resin (A2). Alternatively, a hydroxyl-containing acrylate copolymer (A1) having a different monomer composition may be added. Also possible is the addition of a mixture of different acrylate copolymers (A1) and/or polyester resins (A2) with possibly one resin having the same monomer composition as the acrylate copolymer (A1) synthesized in the presence of the polyester resin (A2).
As the polyurethane resin (A3) for use in accordance with the invention, containing hydroxyl and acid groups, suitable resins include all polyurethane resins having the indicated OH numbers, acid numbers, molecular weights, and viscosities.
Suitable polyurethane resins (A3) are described, for example, in the following documents: EP-A-355 433, DE-A-35 45 618, DE-A-38 13 866, DE-A-32 10 051, DE-A-26 24 442, DE-A-37 39 332, U.S. Pat. No. 4,719,132, EP-A-0 089 497, U.S. Pat. No. 4,558,090, U.S. Pat. No. 4,489,135, DE-A-36 28 124, EP-A-0 158 099, DE-A-29 26 584, EP-A-0 195 931, DE-A-33 21 180 and DE-A-40 05 961.
In component (I) it is preferred t o us e polyurethane resins (A3) which are preparable by reacting isocyanato-containing prepolymers with compounds that are reactive toward isocyanate groups.
The preparation of isocyanato-containing prepolymers may take place by reacting polyols having a hydroxyl number of from 10 to 1800, preferably from 50 to 1200 mg KOH/g, with excess polyisocyanates at temperatures of up to 150xc2x0 C., preferably from 50 to 130xc2x0 C., in organic solvents which are unable to react with isocyanates. The equivalence ratio of NCO to OH groups is situated between 2.0:1.0 and  greater than 1.0:1.0, preferably between 1.4:1 and 1.1:1.
The polyols used to prepare the prepolymer may be of low molecular weight and/or high molecular weight and may contain groups that are slow to react and are anionic or capable of forming anions. It is also possible to use low molecular weight polyols having a molecular weight of from 60 up to 400 daltons to prepare the isocyanato-containing prepolymers. In this case amounts of up to 30% by weight of the overall polyol constituents are used, preferably from about 2 to 20% by weight.
In order to obtain an NCO prepolymer of high flexibility, a high fraction of a predominantly linear polyol having a preferred OH number of from 30 to 150 mg KOH/g should be added. Up to 97% by weight of the overall polyol may consist of saturated and unsaturated polyesters and/or polyethers having a number average molecular weight Mn of from 400 to 5000 daltons. The selected polyetherdiols should not introduce excessive amounts of ether groups, since otherwise the polymers formed start to swell in water. Polyesterdiols are prepared by esterifying organic dicarboxylic acids or their anhydrides with organic diols, or derive from a hydroxycarboxylic acid or from a lactone. In order to prepare branched polyester polyols, it is possible to employ a minor proportion of polyols or polycarboxylic acids having a higher functionality.
The alcohol component used to prepare the polyurethane resins preferably consists at least to a certain extent of
u1) at least one diol of the formula (Ixe2x80x2) 
xe2x80x83in which R1 and R2 are each an identical or different radical and are an alkyl radical having from 1 to 18 carbon atoms, an aryl radical or a cycloaliphatic radical, with the proviso that R1 and/or R2 must not be methyl, and/or
u2) at least one diol of the formula (IIxe2x80x2) 
xe2x80x83in which R3, R4, R6 and R7 are each identical or different radicals and are an alkyl radical having from 1 to 6 carbon atoms, a cycloalkyl radical or an aryl radical and R5 is an alkyl radical having from 1 to 6 carbon atoms, an aryl radical or an unsaturated alkyl radical having from 1 to 6 carbon atoms, and n is either 0 or 1.
Suitable diols (u1) are all propanediols of the formula (Ixe2x80x2) in which either R1 or R2 or R1 and R2 is or are other than methyl, such as 2-butyl-2-ethyl-1,3-propanediol, 2-butyl-2-methyl-1,3-propanediol, 2-phenyl-2-methyl-1,3-propanediol, 2-propyl-2-ethyl-1,3-propanediol, 2-di-tert-butyl-1,3-propanediol, 2-butyl-2-propyl-1,3-propanediol, 1-dihydroxymetbylbicyclo-[2.2.]heptane, 2,2-diethyl-1,3-propanediol, 2,2-dipropyl-1,3-propanediol, 2-cyclohexyl-2-methyl-1,3-propanediol, et cetera, for example.
Examples of diols (u2) (formula (IIxe2x80x2)) that may be used include 2,5-dimethyl-2,5-hexanediol, 2,5-diethyl-2,5-hexanediol, 2-ethyl-5-methyl-2,5-hexanediol, 2,4-dimethyl-2,4-pentanediol, 2,3-dimethyl-2,3-butanediol, 1,4-bis(2xe2x80x2-hydroxypropyl)benzene, and 1,3-bis(2xe2x80x2-hydroxypropyl)benzene.
As diols (u1) it is preferred to use 2-propyl-2-ethyl-1,3-propanediol, 2,2-diethyl-1,3-propanediol, 2-butyl-2-ethyl-1,3-propanediol, and 2-phenyl-2-ethyl-1,3-propanediol, and as component (u2) it is preferred to use 2,3-dimethyl-2,3-butanediol and also 2,5-dimethyl-2,5-hexanediol. Particular preference is given to using 2-butyl-2-ethyl-1,3-propanediol and also 2-phenyl-2-ethyl-1,3-propanediol as component (u1) and 2,5-dimethyl-2,5-hexanediol as component (u2).
The diols (u1) and/or (u2) are commonly used in an amount of from 0.5 to 15% by weight, preferably from 1 to 7% by weight, based in each case on the overall weight of the synthesis components used to prepare the polyurethane resins (A3).
Typical multifunctional isocyanates used to prepare the polyurethane resins (A3) are aliphatic, cycloaliphatic and/or aromatic polyisocyanates containing at least two isocyanate groups per molecule. Preference is given to the isomers or isomer mixtures of organic diisocyanates. Owing to their good stability to ultraviolet light, (cyclo)aliphatic diisocyanates give rise to products having a low tendency to yellow. The polyisocyanate component used to form the prepolymer may also contain a fraction of polyisocyanates of higher functionality, provided that no gelling is caused as a result. Products which have become established as triisocyanates are those formed by trimerization or oligomerization of diisocyanates or by reaction of diisocyanates with polyfunctional compounds containing OH or NH groups. The average functionality may be lowered if desired by adding monoisocyanates.
Examples of polyisocyanates that may be used include phenylene diisocyanate, tolylene diisocyanate, xylylene diisocyanate, bisphenylene diisocyanate, naphthylene diisocyanate, diphenylmethane diisocyanate, isophorone diisocyanate, cyclobutane diisocyanate, cyclopentylene diisocyanate, cyclohexylene diisocyanate, methylcyclohexylene diisocyanate, dicyclohexylmethane diisocyanate, ethylene diisocyanate, trimethylene diisocyanate, tetramethylene diisocyanate, pentamethylene diisocyanate, hexamethylene diisocyanate, propylene diisocyanate, ethylethylene diisocyanate, and trimethylhexane diisocyanate.
To prepare high-solids polyurethane solutions (A3), use is made in particular of diisocyanates of the general formula (IIIxe2x80x2) 
where x is a divalent aromatic hydrocarbon radical, preferably an unsubstituted or halogen-, methyl- or methoxy-substituted naphthylene, diphenylene or 1,2-, 1,3- or 1,4-phenylene radical, with particular preference a 1,3-phenylene radical and R1 and R2 are an alkyl radical having 1-4 carbon atoms, preferably a methyl radical. Diisocyanates of the formula (IIIxe2x80x2) are known (their preparation is described, for example, in EP-A-101 832, U.S. Pat. No. 3,290,350, U.S. Pat. No. 4,130,577, and U.S. Pat. No. 4,439,616) and some are available commercially (1,3-bis(2-isocyanatoprop-2-yl)benzene, for example, is sold by the American Cyanamid company under the tradename TMXDI (META)(copyright)).
Further preferred as polyisocyanate components are diisocyanates of the formula (IVxe2x80x2): 
where:
R is a divalent alkyl or aralkyl radical having from 3 to 20 carbon atoms and Rxe2x80x2 is a divalent alkyl or aralkyl radical having from 1 to 20 carbon atoms;
especially 1-isocyanato-2-(3-isocyanatoprop-1-yl)cyclohexane.
Polyurethanes are generally incompatible with water unless specific constituents are incorporated and/or special preparation steps taken in the course of their synthesis. To prepare the polyurethane resins (A3) it is thus possible to use compounds which contain two H-active groups that are reactive with isocyanate groups, and at least one group which ensures dispersibility in water. Suitable groups of this kind are nonionic groups (e.g., polyethers), anionic groups, mixtures of these two groups, or cationic groups.
Accordingly it is possible to build into the polyurethane resin (A3) an acid number which is sufficiently large that the neutralized product can be dispersed safely in water. For this purpose use is made of compounds containing at least one isocyanate-reactive group and at least one group capable of forming anions. Suitable isocyanate-reactive groups are, in particular, hydroxyl groups and also primary and/or secondary amino groups. Groups capable of forming anions are carboxyl, sulfonic acid and/or phosphonic acid groups. It is preferred to use alkanoic acids having two substituents on the alpha carbon atom.
The substituent may be a hydroxyl group, an alkyl group or an alkylol group. These polyols have at least one, generally from 1 to 3, carboxyl groups in the molecule. They have from 2 to about 25, preferably from 3 to 10 carbon atoms. The carboxyl-containing polyol may account for from 3 to 100% by weight, preferably from 5 to 50% by weight, of the overall polyol constituent in the NCO prepolymer.
The amount of ionizable carboxyl groups that is available by virtue of the carboxyl group neutralization in salt form is generally at least 0.4% by weight, preferably at least 0.7% by weight, based on the solids. The upper limit is approximately 12% by weight. The amount of dihydroxyalkanoic acids in the unneutralized prepolymer gives an acid number of at least 5 mg KOH/g, preferably at least 10 mg KOH/g. With very low acid numbers, it is generally necessary to take further measures to achieve dispersibility in water. The upper limit on the acid number is 150 mg KOH/g, preferably 40 mg KOH/g, based on the solids. The acid number is preferably situated within the range from 20 to 40 mg KOH/g.
The isocyanate groups of the isocyanato-containing prepolymer are reacted with a modifier. The modifier is preferably added in an amount such that instances of chain extension and thus of molecular weight increase occur. Modifiers used are preferably organic compounds containing hydroxyl and/or secondary and/or primary amino groups, especially polyols with a functionality of two, three and/or more. Examples of polyols which can be used include trimethylolpropane, 1,3,4-butanetriol, glycerol, erythritol, mesoerythritol, arabitol, adonitol, etc. Trimethylolpropane is used with preference.
To prepare the polyurethane resin (A3) it is preferred first to prepare an isocyanato-containing prepolymer from which the desired polyurethane resin (A3) is then prepared by further reaction, preferably chain extension. The reaction of the components takes place in accordance with the well-known processes of organic chemistry (cf., e.g., Kunststoff-Handbuch, Volume 7: Polyurethane, edited by Dr. Y. Oertel, Carl Hanser Verlag, Munich, Vienna, 1983). Examples of the preparation of the prepolymers are described in DE-A 26 24 442 and DE-A 32 10 051. The polyurethane resins (A3) may be prepared by the known methods (e.g., acetone method).
The components are preferably reacted in ethoxyethyl propionate (EEP) as solvent. The amount of EEP in this case may be variable within wide limits and should be sufficient for the formation of a prepolymer solution of appropriate viscosity. In general up to 70% by weight, preferably from 5 to 50% by weight, and with particular preference less than 20% by weight of solvent is used, based on the solids. Accordingly, the reaction may be carried out with very particular preference for example, at a solvent content of 10-15% by weight EEP, based on the solids.
The reaction of the components may take place if desired in the presence of a catalyst, such as organotin compounds and/or tertiary amines.
To prepare the prepolymers, the amounts of the components are chosen such that the equivalents ratio of NCO groups to OH groups is situated between 2.0:1.0 and  greater than 1.0:1.0, preferably between 1.4:1 and 1.1:1.
The NCO prepolymer contains at least about 0.5% by weight of isocyanate groups, preferably at least 1% by weight of NCO, based on the solids. The upper limit is approximately 15% by weight, preferably 10% by weight, with particular preference 5% by weight of NCO.
In particular, the especially preferred component (I) comprises as binder (A)
(A1) at least 20% by weight of at least one acrylate copolymer (A1),
(A2) from 0 to 30% by weight of at least one polyester resin (A2),
(A3) from 0 to 80% by weight of at least one polyurethane resin (A3), and
(A4) from 0 to 10% by weight of at least one further binder (A),
the sum of the weight fractions of components (A1) to (A4) being in each case 100% by weight.
Besides the binders (A), the component (I) may include as constituent (B) all customary coatings pigments and/or fillers in fractions of from 0 to 60% by weight, based on component (I). In this context it is possible to use not only the pigments that are common in aqueous coating compositions and which do not react with water and/or do not dissolve in water, but also the pigments commonly employed in conventional coating compositions. The pigments may comprise organic or inorganic compounds and may impart color and/or effect. The coating composition of the invention therefore ensures, owing to this large number of appropriate pigments, a universal scope for use, and permits the realization of a large number of shades.
As effect pigments it is possible to use metal flake pigments, such as commercially customary aluminum bronzes, aluminum bronzes chromated in accordance with DE-A-36 36 183, and commercially customary stainless steel bronzes, and also nonmetallic effect pigments, such as pearlescent pigments and interference pigments for example. Examples of suitable inorganic color pigments are titanium dioxide, iron oxides, Sicotrans yellow, and carbon black. Examples of suitable organic color pigments are indanthrene blue, Cromophthal red, Irgazine orange and Heliogen green. Examples of suitable fillers are chalk, calcium sulfates, barium sulfate, silicates such as talc or kaolin, silicas, oxides such as aluminum hydroxide or magnesium hydroxide, nanoparticles or organic fillers such as textile fibers, cellulose fibers, polyethylene fibers or wood flour.
As a further constituent (C) the component (I) may include at least one organic solvent which can be diluted with water. Such solvents may also participate in the reaction with the crosslinking component (II) and may therefore act as reactive diluents. Examples of suitable solvents or reactive diluents are those specified above.
Also suitable as solvents are esters, ketones, keto esters, glycol ethers such as ethylene, propylene or butylene glycol ethers, glycol esters such as ethylene, propylene or butylene glycol esters, or glycol ether esters such as ethoxyethyl propionate and isopropoxypropanol. Further suitable solvents include aliphatic and aromatic solvents such as dipentene, xylene or Shellsol(copyright).
As constituent (D) the component (I) comprises, if desired, at least one neutralizing agent.
Examples of suitable neutralizing agents for functional groups (i) which can be converted into cations are organic and inorganic acids such as sulfuric acid, hydrochloric acid, phosphoric acid, formic acid, acetic acid, lactic acid, dimethylolpropionic acid or citric acid.
Examples of suitable neutralizing agents for functional groups (ii) which can be converted into anions are ammonia, ammonium salts, such as ammonium carbonate or ammonium hydrogen carbonate, for example, and also amines, such as trimethylamine, triethylamine, tributylamine, dimethylaniline, diethylaniline, triphenylamine, dimethylethanolamine, diethylethanolamine, methyldiethanolamine, triehlianolamine, and the like. Neutralization may be effected in organic phase or in aqueous phase. Dimethylethanolamine is a preferred neutralizing agent used.
The amount of neutralizing agent (D) used in total in the coating composition of the invention is chosen such that from 1 to 100 equivalents, preferably from 50 to 90 equivalents, of the functional groups (i) or (ii) of the binder (A) are neutralized. The neutralizing agent (D) may be added to component (I), (II) and/or (III) or during the preparation of component (IV) before it is dried. Preferably, however, the neutralizing agent (D) is added to component (III).
As constituent (E) the component (I) may comprise at least one rheology control additive. Examples of suitable rheology control additives are those known from the patents WO 94/22968, EP-A-0 276 501, EP-A-0 249 201, and WO 97/12945; crosslinked polymeric microparticles, as disclosed for example in EP-A-0 008 127; inorganic phyllosilicates such as aluminum magnesium silicates, sodium magnesium phyllosilicates, and sodium magnesium fluorine lithium phyllosilicates of the montmorillonite type; silicas such as Aerosils; or synthetic polymers containing ionic and/or associative groups, such as polyvinyl alcohol, poly(meth)acrylamide, poly(meth)acrylic acid, polyvinylpyrrolidone, styrene-maleic anhydride or ethylene maleic anhydride copolymers and their derivatives, or hydrophobically modified ethoxylated urethanes or polyacrylates. Preferred rheology control additives used are polyurethanes.
The component (I) may further comprise at least one additional customary coatings additive (E). Examples of such additives are defoamers, dispersing auxiliaries, emulsifiers, and leveling agents.
Of course, said additives (E) may also be added separately to the coating composition. In this case the additives (E) are then referred to as component (V).
To prepare the coating compositions of the invention it is preferred to use components (I) which consist of
from 20 to 90% by weight, preferably from 35 to 80% by weight, of the binder (A), especially the polymeric or oligomeric resins (A1), (A2), (A3), and/or (A4),
from 0 to 60% by weight of at least one pigment and/or filler (B),
from 0 to 50% by weight, preferably from 10 to 40% by weight, of at least one organic, optionally water-dilutable solvent and/or reactive diluent
from 0 to 20% by weight, preferably from 0.1 to 10% by weight, of at least one neutralizing agent (D), and
from 0 to 20% by weight, preferably from 2 to 10% by weight, of at least one customary auxiliary and/or additive (coatings additive) (E),
the sum of the weight fractions of all the constituents being in each case 100% by weight.
The further key constituent of the coating composition of the invention is at least one crosslinking agent (F), which is present in component (II).
The crosslinking agents (F) comprise at least one diisocyanate and/or polyisocyanate (F) which if desired is dispersed or dissolved in one or more organic, optionally water-dilutable solvents.
The polyisocyanate component (F) comprises organic polyisocyanates, especially those known as paint polyisocyanates, containing free isocyanate groups attached to aliphatic, cycloaliphatic, araliphatic and/or aromatic moieties. Preference is given to using polyisocyanates containing from 2 to 5 isocyanate groups per molecule and having viscosities of from 100 to 10,000, preferably from 100 to 5000, and, where manual mixing of the components (I), (II) and (III) is envisagedxe2x80x94in particular from 5000 to 2000 mPas (at 23xc2x0 C.). If desired, small amounts of organic solvent (G) may be added to the polyisocyanates, preferably from 1 to 25% by weight based on straight polyisocyanate, in order thus to improve the ease of incorporation of the isocyanate and, where appropriate, to lower the viscosity of the polyisocyanate to a level within the aforementioned ranges. Examples of suitable solvent additives for (G) the polyisocyanates are ethoxyethyl propionate, amyl methyl ketone, and butyl acetate. Furthermore, the polyisocyanates may have been conventionally hydrophilically or hydrophobically modified.
Examples of suitable isocyanates are described by way of example in xe2x80x9cMethoden der organischen Chemiexe2x80x9d, Houben-Weyl, Volume 14/2, 4th Edition, Georg Thieme Verlag, Stuttgart 1963, pages 61 to 70, and by W. Siefken, Liebigs Annalen der Chemie, Volume 562, pages 75 to 136. Suitable examples include the isocyanates specified in the description of the polyurethane resins (A3), and/or isocyanato-containing polyurethane prepolymers which may be prepared by reacting polyols with an excess of polyisocyanates and which are preferably of low viscosity.
Further examples of suitable polyisocyanates are isocyanato-containing polyurethane prepolymers which can be prepared by reacting polyols with an excess of polyisocyanates and are preferably of low viscosity. It is also possible to use polyisocyanates containing isocyanurate, biuret, allophanate, iminooxadiazindione, urethane, urea and/or uretdione groups. Polyisocyanates containing urethane groups, for example, are obtained by reacting some of the isocyanate groups with polyols, such as trimethylolpropane and glycerol, for example. It is preferred to use aliphatic or cycloaliphatic polyisocyanates, especially hexamethylene diisocyanate, dimerized and trimerized hexamethylene diisocyanate, isophorone diisocyanate, 2-isocyanatopropylcyclohexyl isocyanate, dicyclohexylmethane 2,4xe2x80x2-diisocyanate, dicyclohexylmethane 4,4xe2x80x2-diisocyanate or 1,3-bis-(isocyanatomethyl)cyclohexane, diisocyanates derived from dimer fatty acids, as sold under the commercial designation DDI 1410 by Henkel, 1,8-diisocyanato-4-isocyanatomethyloctane, 1,7-diisocyanato-4-isocyanatomethylheptane or 1-isocyanato-2-(3-isocyanatopropyl)-cyclohexane, or mixtures of these polyisocyanates.
Very particular preference is given to using mixtures of polyisocyanates containing uretdione and/or isocyanurate and/or allophanate groups and based on hexamethylene diisocyanate, as formed by catalytic oligomerization of hexamethylene diisocyanate using appropriate catalysts. The polyisocyanate constituent may further comprise any desired mixtures of the free polyisocyanates exemplified.
The coating composition of the invention may further comprise isocyanato-free crosslinking agents (Fxe2x80x2). Depending on their reactivity, these may be present in components (I), (II) and/or (III); the critical factor is that the crosslinking agents (Fxe2x80x2) do not adversely affect the storage stability of the component in question, such as by premature crosslinking. The skilled worker will therefore be able to select the appropriate combinations of crosslinking agents (Fxe2x80x2) on the one hand and components (I), (II) and/or (III) on the other in a simple manner.
Examples of suitable crosslinking agents (Fxe2x80x2) are blocked diisocyanates and/or polyisocyanates based on the aforementioned diisocyanates and/or polyisocyanates (F). Examples of suitable blocking agents are aliphatic, cycloaliphatic or araliphatic monoalcohols such as methyl, butyl, octyl or lauryl alcohol, cyclohexanol or phenylcarbinol; hydroxylamines such as ethanolamine; oximes such as methyl ethyl ketone oxime, acetone oxime or cyclohexanone oxime; amines such as dibutylamine or diisopropylamine; CH-acidic compounds such as malonic diesters or ethyl acetoacetate; heterocycles such as dimethylpyrazole; and/or lactams such as epsilon-caprolactam. These crosslinking agents (Fxe2x80x2) may be present in components (I), (II) and/or (III).
Further examples of suitable crosslinking agents (Fxe2x80x2) are polyepoxides (Fxe2x80x2), especially all known aliphatic and/or cycloaliphatic and/or aromatic polyepoxides, based for example on bisphenol A or bisphenol F. Examples of suitable polyepoxides (Fxe2x80x2) also include the polyepoxides available commercially under the designations Epikote(copyright) from Shell, Denacol(copyright) from Nagase Chemicals Ltd., Japan, such as Denacol EX-411 (pentaerythritol polyglycidyl ether), Denacol EX-321 (trimethylolpropane polyglycidyl ether), Denacol EX-512 (polyglycerol polyglycidyl ether), and Denacol EX-521 (polyglycerol polyglycidyl ether). These crosslinking agents (Fxe2x80x2) may be present in components. (I) and/or (III).
As crosslinking agents (Fxe2x80x2) it is also possible to use tris(alkoxycarbonylamino)triazines of the formula 
These crosslinking agents (Fxe2x80x2) may be present in components (I) and/or (III).
Examples of suitable tris(alkoxycarbonylamino)triazines (Fxe2x80x2) are described in the patents U.S. Pat. No. 4,939,213, U.S. Pat. No. 5,084,541, and EP-A-0 624 577. The tris(methoxy-, tris(butoxy- and/or tris(2-ethylhexoxycarbonylamino)-triazines are used in particular.
The methyl butyl mixed esters, the butyl 2-ethylhexyl mixed esters, and the butyl esters are of advantage. They have the advantage over the straight methyl ester of better solubility in polymer melts, and also have less of a tendency to crystallize out.
In particular it is possible to use amino resins, examples being melamine resins, as crosslinking agents (Fxe2x80x2). In this context it is possible to use any amino resin suitable for transparent topcoat materials or clearcoat materials, or a mixture of such amino resins. Particularly suitable are the customary and known amino resins some of whose methylol and/or methoxymethyl groups have been defunctionalized by means of carbamate or allophanate groups. Crosslinking agents of this type are described in the patents U.S. Pat. No. 4,710,542 and EP-B-0 245 700 and also in the article by B. Singh and coworkers, xe2x80x9cCarbamylmethylated Melamines, Novel Crosslinkers for the Coatings Industryxe2x80x9d in Advanced Organic Coatings Science and Technology Series, 1991, Volume 13, pages 193 to 207. These crosslinking agents (Fxe2x80x2) may be present in components (I) and/or (III).
Further examples of suitable crosslinking agents (Fxe2x80x2) are beta-hydroxyalkylamides such as N,N,Nxe2x80x2,Nxe2x80x2-tetrakis-(2-hydroxyethyl)adipamide or N,N,Nxe2x80x2,Nxe2x80x2-tetrakis(2-hydroxypropyl)adipamide. These crosslinking agents (Fxe2x80x2) may be present in components (I) and/or (III).
Further examples of suitable crosslinking agents (Fxe2x80x2) are siloxanes, especially siloxanes containing at least one trialkoxy- or dialkoxysilane group. These crosslinking agents (Fxe2x80x2) may be present in components (I), (II) and/or (III).
The polyisocyanates (F) are used advantageously in an amount of at least 70% by weight, with particular preference in an amount of 80 to 100% by weight, based on the overall weight of the crosslinking agents (F) and (Fxe2x80x2) in the coating composition of the invention.
The constituents (G) and (H) of component (II) correspond to the above-described constituents (C) and (E) of component (I), except that here constituents are used which do not react with isocyanate groups.
To prepare the coating compositions of the invention it is preferred to use components (II) which consist of
(F) from 50 to 100% by weight, preferably from 60 to 90% by weight, of at least one crosslinking agent,
(G) from 0 to 50% by weight, preferably from 10 to 40% by weight, of at least one organic, optionally water-dilutable solvent, and
(H) from 0 to 20% by weight, preferably from 0 to 10% by weight, of at least one customary auxiliary and/or (coatings) additive,
the sum of the weight fractions of components (P) to (H) being in each case 100% by weight.
The further key constituent of the coating composition of the invention is component (III).
In accordance with the invention, this component (III) consists of or comprises water. It is of advantage in accordance with the invention if the component (III) includes further suitable constituents in addition to water. It is substantially free of acrylate copolymers (A) dispersed or dissolved in it.
Examples of suitable constituents are the binders (A) described in detail above, especially the binders (A) containing
(i) functional groups which can be converted into cations by neutralizing agents and/or quaternizing agents, and/or cationic groups,
or
(ii) functional groups which can be converted into anions by neutralizing agents, and/or anionic groups,
and/or
(iii) nonionic hydrophilic groups,
with the exception of acrylate copolymers (A).
Of these binders (A), the binders (A2) and/or (A3) and, where appropriate, (A4) dispersed or dissolved in water are particularly advantageous and therefore used with particular preference.
Where component (I) includes binders (A) which are not, or not to any great extent, soluble or dispersible in water, it is advisable to use in particular the binders (A2) and/or (A3) that are dispersed or dissolved in water.
Alternatively, the binders (A) may be in the form of a powder slurry. In this case flame retardants (Fxe2x80x2) may also be present in the powder slurry particles. Powder slurries are customary and known and are described, for example, in the patents EP-A-0 652 264, U.S. Pat. No. 4,268,542, DE-A-196 13 547, and DE-A-195 18 392.
The component (III) may further comprise at least one of the above-described reactive diluents.
For preparing the coating compositions of the invention it is very particularly preferred to use components (III) which consist of
(J) from 40 to 90% by weight, preferably from 50 to 85% by weight, of water,
(K) from 5 to 50% by weight, preferably from 10 to 45% by weight, of the binder (A), especially the polymeric or oligomeric resins (A2) and/or (A3) and, where appropriate (A4), in a form dissolved or dispersed in water,
(L) from 0 to 20% by weight, preferably from 2 to 10% by weight, of at least one neutralizing agent, and
(M) from 0 to 20% by weight, preferably from 2 to 10% by weight, of at least one customary auxiliary and/or (coatings) additive,
the sum of the weight fractions of components (J) to (M) being in each case 100% by weight.
The constituents (L) and (M) of component (III) correspond to the constituents (D) and (E) of component (I), described above.
The component (III), consisting of an aqueous dispersion of the binders (A) and particularly of the binders (A2) and/or (A3) and, where appropriate, (A4), may on the one hand be prepared by preparing the binders (A) in organic solvents, then neutralizing the acid groups, especially carboxyl groups, with the neutralizing agent (L) and, finally, introducing the neutralized constituents into deionized water, or on the other hand may be prepared by emulsion polymerization of the monomeric building blocks of the binders (A) in water.
Preferably, the components (A2) and/or (A3) and, where appropriate, (A4) are first prepared in organic solvents, then neutralized and, finally, dispersed in water in neutralized form.
Examples of suitable neutralizing agents (L) are the ammonia, ammonium salts and amines (constituent (D) of component (I)) already described in connection with the preparation of component (I), it being possible for the neutralization to take place in organic phase or in aqueous phase. The total amount of neutralizing agent (L) used to neutralize the-binders (A) is chosen so that from 1 to 100 equivalents, preferably from 50 to 90 equivalents, of the acid groups of the binders (A) are neutralized.
Furthermore, the coating composition of the invention may, based on its overall amount, contain up to 40% by weight of constituents (N) which are curable with. actinic light, especially UV radiation, and/or electron beams. These constituents may be present in component (I), (II) and/or (III), in particular in component (I). This has the advantage that the coating compositions of the invention are thermally curable and/or radiation-curable
Suitable constituents (N) include in principle all low molecular mass, oligomeric, and polymeric compounds which are curable with actinic light and/or electron beams, such compounds being those as are commonly used in the field of UV-curable or electron-beam-curable coating compositions. These radiation-curable coating compositions normally include at least one, preferably two or more, radiation-curable binders, based in particular on ethylenically unsaturated prepolymers and/or ethylenically unsaturated oligomers, optionally one or more reactive diluents, and optionally one or more photoinitiators.
It is advantageous to use the radiation-curable binders as constituents (N). Examples of suitable radiation-carable binders (N) are (meth)acryloyl-functional (meth)acrylic copolymers, polyether acrylates, polyester acrylates, unsaturated polyesters, epoxy acrylates, urethane acrylates, amino acrylates, melamine acrylates, silicone acrylates, and the corresponding methacrylates. It is preferred to use binders (N) which are free from aromatic structural units. Preference is therefore given to using urethane (meth)acrylates and/or polyester (meth)acrylates, with particular preference aliphatic urethane acrylates.
To prepare the coating compositions, components (I), (II), (III) and (IV) are used preferably in amounts such that the equivalents ratio of isocyanate-reactive groups of the binders (A) and of the reactive diluents to the crosslinking groups of the crosslinking agent (F) and also, where appropriate, (Fxe2x80x2) is situated between 1:2 and 2:1, preferably between 1:1.2 and 1:1.5.
Furthermore, the coating compositions of the invention preferably comprise in total
from 15 to 60% by weight, preferably from 20 to 50% by weight, of binders (A),
from 5 to 30% by weight, preferably from 10 to 20% by weight, of crosslinking agents (F),
from 3 to 25% by weight, preferably from 10 to 20% by weight, of organic solvents (C),
from 25 to 60% by weight, preferably from 30 to 50% by weight, of water,
from 0 to 50% by weight, preferably from 0 to 30% by weight, of pigments and/or fillers (B),
from 0 to 10% by weight of customary coatings additives (E), and
from 0 to 40% by weight, preferably from 0 to 30% by weight, of constituents (N) curable with actinic light, especially UV radiation, and/or electron beams,
based in each case on the overall weight of the coating composition of the invention.
The preparation of component (I) takes place in accordance with methods known to the skilled worker by mixing and, where appropriate, dispersing of the individual constituents. For example, color pigments (B) are normally incorporated by grinding (dispersing) the respective pigments in one or more binders. The dispersing of the pigments takes place with the aid of customary apparatus, such as bead mills and sand mills, for example.
Components (II) and (III) and, where appropriate, (V) are likewise prepared in accordance with methods well known to the skilled worker, by mixing and/or dispersing the individual constituents.
The coating compositions of the invention are prepared in particular by the following mixing method from components (I), (II), (III) and (IV):
In a first process step, at least one component (I) is mixed with at least one component (II) to give the mixture (I/II). In a second process step, at least one component (III) is mixed with at least one component (IV) to give the mixture (III/IV). In a third process step, either the mixture (I/II) is dispersed and/or dissolved in the mixture (III/IV) or the mixture (III/IV) is dispersed and/or dissolved in the mixture (I/II).
In this process, the neutralizing agent (L) may already be present in components (I), (III) and/or (IV), or may be added to the mixtures (I/II) and/or (III/IV) or to the coating composition (I/II/III/IV) of the invention.
If binders (A) containing exclusively nonionic hydrophilic groups (iii) are used, the use of the neutralizing agents (L) is omitted.
The coating compositions of the invention may be applied to any desired substrates, such as metal, wood, plastic, glass or paper, for example, by customary application methods, such as spraying, knife coating, brushing, flow coating, dipping or rolling, for example.
When used in automotive refinish, the coating compositions of the invention are normally cured at temperatures below 120xc2x0 C., preferably at temperatures of not more than 80xc2x0 C. When they are used in automotive OEM finishing it is also possible to employ higher curing temperatures.
The coating compositions of the invention are preferably used to produce topcoats. The coating compositions of the invention may be used both in the OEM finishing and in the refinish of automobile bodies. However, they are preferably used in the area of refinish and the finishing of plastics parts.
The aqueous coating compositions of the invention may be used as primer-surfacers and also to produce singlecoat topcoats, and also as pigmented basecoat materials or, in particular, as clearcoat materials in a process for producing a multicoat system (basecoat/clearcoat process).